Semiconductor device fabricating system and semiconductor device fabricating method

ABSTRACT

Shutoff valves are placed in parts of the process gas supply lines at positions near the processing vessel. A main purge gas supply line branches into branch purge gas supply lines, each of which is provided with an orifice called sonic nozzle. The branch purge gas supply lines are connected to parts of the process gas supply lines extending between the shutoff valves and the processing vessel. The ratio P1/P2, where P1 is primary pressure on the primary side of the orifice and P2 is secondary pressure on the secondary side of the orifice, is controlled to be not less than a predetermined value, for example, two, thereby, the purge gas can always be supplied at equal flow rates into the process gas supply lines. The total flow rate of the purge gas is controlled by a mass flow controller placed in the main purge gas supply line.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device fabricating method of processing a substrate on which semiconductor devices are to be fabricated in a processing vessel by supplying a process gas into the processing vessel and a semiconductor fabricating system for carrying out the semiconductor device fabricating method.

2. Description of the Related Art

Some semiconductor device fabricating methods carry out predetermined processes continuously to process a substrate in a processing vessel and a cleaning process for cleaning the interior of the processing vessel by selectively supplying process gases and cleaning gases through a plurality of gas supply lines connected to the processing vessel. If a process gas supplied through the open gas supply line into the processing vessel flows into the other closed gas supply lines not supplying the gases, it is possible that a product is deposited in the closed gas supply lines causing contamination with particles or the gas supply lines are corroded. Therefore, it Is important to supply a purge gas into the closed gas supply lines to prevent the backflow of a reaction gas from the processing vessel into the closed gas supply lines. Such a backflow preventing method is disclosed in JP4-24921A.

The prior art backflow preventing method supplies a purge gas through pipes connected to closed process gas supply pipes not carrying process gases during a process for forming a film on a surface of a substrate by supplying process gases through process gas supply pipes into a processing vessel to prevent the diffusion of the process gases supplied into the processing vessel into the closed process gas supply lines. When a purge gas, such as an inert gas, is supplied into the closed process gas supply pipes, the process gas supplied into the processing vessel is diluted by the purge gas supplied into the closed process gas supply pipes. Therefore, it is desirably to supply the purge gas always at a predetermined flow rate into the closed process gas supply pipes regardless of the number of the closed process supply pipes to maintain a predetermined process gas concentration in the processing vessel. Moreover, the purge gas must be supplied into the closed process gas supply pipes at a flow rate not lower than a predetermined flow rate. Nothing about this requirement is mentioned in JP4-24921A.

The inventors of the present invention proposed piping systems shown in FIGS. 6 to 9 to solve the foregoing problems.

The piping system shown in FIG. 6 includes a processing vessel 100 included in a vertical thermal processing apparatus, gas supply lines 101, 102 and 103 respectively for supplying process gases A, B and C, and a purge gas supply line 104. Branch lines branching from the purge gas supply line 104 are connected to the process gas supply lines 101, 102 and 103 to supply a purge gas into the closed ones of the process gas supply lines 101, 102 and 103. Mass flow controllers 105 are placed in the gas supply lines 101, 102, 103 and 104 to control the flow rates of gases supplied from gas sources 201 to 204, respectively. In FIG. 6, indicated at V0 is a valve, at V1 to V4 are shutoff valves and at V are valves. The valves above the mass flow controllers are designated by the same reference character V for convenience.

Suppose that the process gas A and the process gas B are used for carrying out a predetermined process, such as a film deposition process in the processing vessel 100. Nitrogen gas, namely, a purge gas, is supplied at a low flow rate through the purge gas supply line 104 into the closed process gas supply line 103 for supplying the process gas C and at a low rate through the purge gas supply line 104. The sum of those flow rates is a predetermined purge gas flow rate.

The flow rates of the purge gas are controlled by the mass flow controllers 105 placed in the gas supply lines 101 to 104. The capacities of the mass flow controllers 105 placed in the gas supply lines 101 to 104 are excessively large to control the low flow rate of the purge gas. The capacities of the mass flow controllers 105 for controlling the flow of the process gases are, for example, 5 l/min. A mass flow controller for controlling the flow of an inert gas has a control capacity of 50 l/min. If the mass flow controller having such a large control capacity of 50 l/min is used for controlling a very low flow rate on the order of 50 cm³/min, the value of a controlled variable is in the range of about 1 to about 2% of the control capacity. Consequently, it is difficult to adjust the flow rate of the inert gas to values in a desired flow rate range and accurate flow rate control cannot be achieved. Therefore, the total purge gas flow rate cannot be accurately controlled, the process gas concentration varies and, consequently, it is possible that the process becomes unstable.

The piping system shown in FIG. 7 has branch lines 107 branched from a purge gas supply line 104, connected to process gas supply lines 101 to 103 and provided with mass flow controllers 106 having a control capacity of, for example 50 cm³/min, respectively. A bypass line 108 is connected to the purge gas supply line 104 and a mass flow controller 106 having a small control capacity is placed in the bypass line 108. The flow of the purge gas supplied to the closed process gas supply lines is controlled by the mass flow controllers 106 to supply the purge gas for purging at a low flow rate into the closed process gas supply lines. Since a total flow rate is the sum of dividual flow rates at which the mass flow controllers 106 control the flow of the purge gas, errors in flow rates controlled by the mass flow controllers 106 are accumulated and hence the accuracy of control of the total flow rate of the purge gas decreases. Since all the branch lines 107 are provided with the mass flow controllers 106, this piping system is costly.

When the process gas supply lines 101 to 103 of the piping system shown in FIG. 7 are selectively opened to carry out processes, such as a first film deposition process and a second film deposition process, continuously, when monoatomic or monomolecular films are formed successively in layers by selectively using process gases, or when a film deposition process is carried out after a cleaning process for cleaning the interior of the processing vessel, a long time is necessary for purging the residual gases remaining in the process gas supply lines. (Note that processes mentioned in this specification include a cleaning process.)

The foregoing problems will be explained with reference to FIGS. 8 and 9. Referring to FIG. 8, the process gases A and B are supplied respectively through the process gas supply lines 101 and 102, and a purge gas is supplied at a low flow rate into the process gas supply line 103 and the purge gas supply line 104 to carry out a first process. Suppose that the valves V connected to the process gas supply lines 101 and 102 are operated to stop supplying the process gases A and B and to start supplying the purge gas at a low flow rate to the process gas supply lines 101 and 102 and the valves connected to the process gas supply line 103 are operated to stop supplying the purge gas into the process gas supply line 103 and to start supplying the process gas C into the process gas supply line 103 to start a second process subsequently to the first process. Then, the process gases remaining in the process gas supply lines 101 and 102 need to be replaced with the purge gas to avoid the adverse effect of the process gases remaining in the process gas supply lines 101 and 102 and diffused into the processing vessel 100 on the second process. After the supply of the process gases A and B through the process gas supply lines 101 and 102 has been stopped, the shutoff valves V1 and V2 are kept open to pas the purge gas at a low flow rate through the process gas supply lines 101 and 102. Therefore, the process gases remaining in the lines extending between the processing vessel 100 and the valves V in a gas box remote from the processing vessel 100 need to be purged, which needs a long time and increases tact time.

SUMMARY OF THE INVENTION

The present invention has been made in view of the foregoing problems and it is therefore an object of the present invention to provide a semiconductor device fabricating method capable of accurately controlling the flow of a purge gas in a process gas supply pipes connected to a processing vessel, and a semiconductor conductor fabricating system for carrying out the semiconductor device fabricating method.

Another object of the present invention is to provide a semiconductor device fabricating method capable of quickly purging a process gas remaining in a process gas supply pipe, and a semiconductor device fabricating system for carrying out the semiconductor device fabricating method.

The present invention provides a semiconductor device fabricating system, which includes: a processing vessel; process gas supply lines each connected to the processing vessel to supply a process gas into the processing vessel; shutoff valves each placed In each of the process gas supply lines at a position adjacent to the processing vessel; a main purge gas supply line for carrying a purge gas; branch purge gas supply lines branched from the main purge gas supply line, each of the branch purge gas supply lines being connected to a part of each of the process gas supply lines extending between the shutoff valve and the processing vessel; a flow controller placed in the main purge gas supply line to control a sum of flow rates at which the purge gas flows through the branch purge gas supply lines; and orifices each placed in each of the branch purge gas supply lines, each of the orifices being configured so that a flow rate of the purge gas flowing through the orifice is determined according to a primary pressure on a primary side of the orifices when pressure ratio P1/P2, where P1 is a primary pressure on the primary side of the orifice, and P2 is a secondary pressure on a secondary side of the orifice, is not smaller than a predetermined value.

In the operation of the semiconductor device fabricating system, the pressure ratio P1/P2 is controlled to be not smaller than the predetermined value, for example, not smaller than two. Thus the purge gas flows through the orifice at a sonic speed and hence the purge gas flowing through the main purge gas supply line can be equally distributed to the branch purge gas supply lines.

The flow controller may be a mass flow controller. In this case, the total flow rate of the purge gas can be controlled accurately.

The flow controller may include a flow measuring device, and a pressure regulating device for regulating the primary pressure P1 on the primary side of the orifices on the basis of a measured flow rate measured by the flow measuring device. The flow measuring device measures the flow rate of the purge gas flowing through the orifices and the primary pressure P1 is controlled always on the basis of the measured flow rate to maintain the primary pressure P1 at a level not lower than the predetermined value.

The prevent invention also provides a semiconductor device fabricating system, which includes: a processing vessel; process gas supply lines each connected to the processing vessel to supply a process gas into the processing vessel; shutoff valves each placed in each of the process gas supply lines at a position adjacent to the processing vessel; a main purge gas supply line for carrying a purge gas; branch purge gas supply lines branched from the main purge gas supply line, each of the branch purge gas supply lines being connected to a part of each of the process gas supply lines extending between the shutoff valve and the processing vessel; and flow controllers each placed in the each of the branch purge gas supply lines to control a flow rate at which the purge gas flows through each of the branch purge gas lines.

According to another aspect of the present invention, there is provided a semiconductor device fabricating method for processing a substrate by a predetermined process in a processing vessel to fabricate semiconductor devices on the substrate by using process gases supplied through process gas supply lines connected to the processing vessel. The method includes: supplying a purge gas through a main purge gas supply line and controlling the flow of the purge gas flowing through the main purge gas supply line; distributing the purge gas flowing through the main purge gas supply line to a plurality of branch purge gas supply lines; passing the purge gas distributed to the branch purge gas supply lines through orifices capable of determining, when pressure ratio P1/P2, where P1 is primary pressure on a primary side of the orifice and P2 is secondary pressure on a secondary side of the orifice, is not smaller than a predetermined value, a flow rate according to the primary pressure P1; supplying the purge gas passed through the orifices to parts of the process gas supply lines extending between the processing vessel and shutoff valves placed in the process gas supply lines at positions near the processing vessel; regulating pressure so that the pressure ratio P1/P2 is not smaller than a predetermined value; and closing at least one of the shutoff valves placed in the process gas supply lines to purge the process gas remaining in a part of the process gas supply line provided with the closed shutoff valve extending below the closed shutoff valve by the purge gas passed through the orifice.

The present invention also provides a semiconductor device fabricating method for processing a substrate by a predetermined process in a processing vessel to fabricate semiconductor devices on the substrate by using process gases supplied through process gas supply lines connected to the processing vessel, the method including the steps of: supplying a purge gas through a main purge gas supply line; distributing the purge gas flowing through the main purge gas supply line to a plurality of branch purge gas supply lines; controlling the flow rate of the purge gas in the branch purge gas supply lines by flow control units respectively placed In the branch purge gas supply lines; supplying the purge gas distributed to each of the branch purge gas supply lines to a part of the process gas supply line at a position between the processing vessel and a shutoff valve placed in a part of the process gas supply line near the processing vessel; and closing the shutoff valve placed in at least one of the process gas supply lines to purge the process gas remaining in a part of this process gas supply line below the shutoff valve by the purge gas passed through the branch purge gas supply line.

According to the present invention, the shutoff valves are placed in parts of the process gas supply lines close to the processing vessel, and the purge gas is supplied to parts of the process gas supply lines each extending between the shutoff valve and the processing vessel. Therefore, only the process gas remaining in the short parts of the process gas supply line extending below the shutoff valve needs to be purged in changing the process, and the residual process gas can be quickly purged. Since the orifice controls the flow of the purge gas flowing through each branch purge gas supply line accurately, the flow controller needs to be placed only in the main purge gas supply line, the total flow rate of the purge gas equal to the sum of the flow rates of the purge gas flowing through the branch purge gas supply lines can be accurately controlled and the process can be stably carried out.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a piping diagram showing a piping system included in a semiconductor device fabricating system in a first embodiment according to the present invention;

FIG. 2 is a schematic view of a shutoff valve included in the piping system shown in FIG. 1;

FIG. 3 is a piping diagram showing the piping system included in the semiconductor device fabricating system shown in FIG. 1;

FIG. 4 is a piping diagram showing a piping system included In a semiconductor device fabricating system in a second embodiment according to the present invention;

FIG. 5 is a piping diagram showing a piping system included in a semiconductor device fabricating system in a third embodiment according to the present invention;

FIG. 6 is a piping diagram showing a piping system included in a first prior art semiconductor device fabricating system;

FIG. 7 is a piping diagram showing a piping system included in second prior art semiconductor device fabricating system;

FIG. 8 is a piping diagram showing a piping system included in a third prior art semiconductor device fabricating system; and

FIG. 9 is a piping diagram showing a piping system included in a fourth prior art semiconductor device fabricating system.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a piping system included, in a vertical thermal processing system, namely, semiconductor device fabricating system, in a first embodiment according to the present invention. The vertical thermal processing system includes, as principal components; a processing vessel 1 for processing a semiconductor wafer, i.e., a substrate on which semiconductor devices are to be fabricated, by a thermal process, such as a film deposition process for depositing a film on the semiconductor wafer (hereinafter, referred to simply as “wafer”); three process gas sources 10, 11 and 12, i.e., a dichlorosilane source 10, an ammonia source 11 and a cleaning gas source 12; process gas supply lines 13, 14 and 15, i.e., a dichlorosilane supply line 13, an ammonia supply line 14 and a cleaning gas supply line 15, respectively connecting the process gas sources 10, 11 and 12 to the processing vessel 1; a discharge line 34 connected to the processing vessel 1; and a purge gas supply unit 5 for supplying a purge gas into the process gas supply lines 13, 14 and 15. A purge gas source 18 is connected to the processing vessel 1 by a purge gas supply line 16 to supply a purge gas into the processing vessel 1 so that pressure in the processing vessel is returned to the atmospheric pressure.

First mass flow controllers 19 are placed in parts of the process gas supply lines 13, 14 and 15 and the purge gas supply line 16 distant from the processing vessel 1, respectively. Shutoff valves V1 to V4 for cutting off gas supply into the processing vessel 1 are placed in parts of the process gas supply lines 13, 14 and 15 and the purge gas supply line 16 near the processing vessel 1.

As shown in FIG. 2, each of the shutoff valves V1 to V4 has a valve body 21 provided with a process gas inlet port 22, a purge gas inlet port 23 and an outlet port 24. The process gas and the purge gas flow respectively through the process gas inlet port 22 and the purge gas inlet port 23 into the valve body 21 and flow out of the valve body 21 through the outlet port 24. When a valve element (not shown) arranged in the valve body 21 is closed, the flow of the process gas is intercepted while the flow of the purge gas is not intercepted. Thus the purge gas flows always through the shutoff valves V1 to V4 placed In the process gas supply lines 13, 14 and 15 and the purge gas supply line 16 into the processing vessel 1.

The construction of the processing vessel 1 will be briefly explained. The processing vessel 1 includes an inner tube 31 having opened opposite ends, and an outer tube 32 having a top wall. A wafer boat 33 supporting a plurality of wafers W in a stack is loaded into a space surrounded by the inner tube 31 from below the inner tube 31. A discharge pipe 34 has one end connected to the outer tube 32 and the other end connected to a vacuum pump 35, namely, an evacuating means. A gas supplied into a lower region in the space surrounded by the inner tube 21 flows upward inside the inner tube 31, flows downward through an annular space between the inner tube 31 and the outer tube 32, and is discharged through the discharge pipe 34.

Although not shown in the drawings, each of the process gas supply lines 13, 14 and 15 and the purge gas supply line 16 is provided with, for example, a particle filter, a pressure sensor, a regulator and such.

The purge gas supply unit 5 is branched off from the purge gas supply line 16. The purge gas supply unit 5 has a main purge gas supply line 50 connected to the purge gas supply line 16, and four branch purge gas supply lines 51 branching off from the main branch gas supply line 50. A second mass flow controller 52 is placed in the main purge gas supply line 50 to control the total flow rate of the purge gas to be distributed to the branch purge gas supply lines 51. A valve 5, a filter F and a pressure sensor PD1 are placed in the main purge gas supply line 50 downstream of the second mass flow controller 52. The respective primary sides of orifices 53 are connected to the branch purge gas supply lines 51, respectively, and the respective secondary sides of the same are connected to parts of the process gas supply lines 13, 14 and 15 and the purge gas supply line 16 extending from the shutoff valves V1 to V4 to the processing vessel 1, respectively. The orifices 53 permit the purge gas to flow at a low flow rate into the supply lines 13 to 16. It appears from FIG. 2 that the branch purge gas supply lines 51 are connected to the shutoff valves V1 to V4. However, actually, a first gas passage formed in the valve body 21 connecting the process gas Inlet port 22 and the outlet port 24 is provided with the not-shown valve element, and a gas second passage formed in the valve body 21 connected to the purge gas inlet port 23 is connected to the first gas passage at a position downstream of the not-shown valve element. Thus, the branch purge gas supply lines 51 are actually connected to parts of the gas supply lines 13 to 16 extending between the shutoff valves V1 to V4 and the processing vessel 1 as shown in the piping diagram of FIG. 1. In the illustrated embodiment, each of the orifices 53 is a metal plate provided with an aperture flaring out downstream and having a maximum diameter of about 70 μm, which is generally called a sonic nozzle. When pressure ratio P1/P2, where P1 is pressure on the primary side of the orifice 53 and P2 is pressure on the secondary side of the orifice 53, is not lower than a predetermined value, such as when the pressure ratio P1/P2 is two or above, the gas flows at a sonic speed through the orifice 53, and the flow rate of the gas flowing through the orifice 53 is dependent on the primary pressure P1. Thus the purge gas flows through the orifices 53 at equal flow rates and the purge gas flowing through the main purge gas supply line 50 is divided into four equal purge gas flows.

The operation of the semiconductor device fabricating device in the first embodiment will be described with reference to FIGS. 1 and 3 on an assumption that a film deposition process for forming a silicon nitride film on a surface of a wafer W using dichlorosilane (SiH₂Cl₂) and ammonia (NH₃) as process gases, a cleaning process for cleaning the interior of the processing vessel 1 using a cleaning gas, such as a mixed gas prepared by mixing fluorine and hydrogen fluoride, and a film deposition process for forming a silicon nitride film are conducted successively in that order.

In FIGS. 1 and 3, dotted arrows indicate flows and flowing directions of gases flowing into the processing vessel 1 and the gas supply lines 13 to 16.

Referring to FIG. 1, a wafer boat 33 holding a plurality of wafers W is loaded into the processing vessel 1, and then a predetermined hot and evacuated atmosphere are created in the processing vessel 1 to start a film forming process. The valves V on the process gas supply lines 13 and 14 are opened to supply dichlorosilane from the dichlorosilane source 10 and to supply ammonia from the ammonia source 11. The mass flow controller 19 on the process gas supply line 13 controls the flow of the dichlorosilane gas such that the dichlorosilane gas flows through the process gas supply line 13 into the processing vessel at, for example, 50 sccm. The mass flow controller 19 on the process gas supply line 14 controls the flow of ammonia gas such that ammonia gas flows through the process gas supply line 14 into the processing vessel 1 at, for example, 500 sccm. At this stage, the valves V on the process gas supply line 15 and the purge gas supply line 16 are kept closed and hence any gases flow through the process gas supply line 15 and the purge gas supply line 16.

The dichlorosilane gas and the ammonia gas interact in the processing vessel 1 to deposit a silicon nitride film on the surface of the wafer W. After the duration of the film forming process for a predetermined time, the valves V on the process gas supply lines 13 and 14 are closed.

The valve V5 on the main purge gas supply line 50 is opened during the film forming process. The primary pressure P1 on the primary side of the orifices 53 is, for example, in the range of about 0.3 to about 0.4 MPa. Pressure in the processing vessel 1 is 133 Pa or below. The pressure in the processing vessel 1 corresponds to the secondary pressure P2 on the secondary sides of the orifices 53. Thus the pressure ratio P1/P2 is in the range of about 2250 and about 3000. The purge gas flows through the orifice 53 at a flow rate corresponding to the primary pressure P1. Therefore, when a desired total flow rate equal to the sum of the flow rates at which the purge gas flows through the branch purge gas supply lines 51 is, for example, 200 sccm, the second mass flow controller 52 controls the flow of the purge gas such that the primary pressure P1 causes the purge gas to flow through the orifices 53 at 50 sccm, Consequently, the purge gas flows through the main purge gas supply line 50 at 200 sccm, the orifices 53 divide the flow of the purge gas accurately into four equal flows of purge gas so that the purge gas flows through the branch purge gas supply line 51 at 50 sccm. Then, the purge gas flows through parts of the gas supply lines 13 to 15 on the secondary side of the shutoff valves V1 to V4 into the processing vessel 1. Even though the process gasses are flowing through the process gas supply lines 13 and 14 and the secondary pressure P2 on the secondary side of the orifices 53 is different from pressures in the process gas supply line 15 and the purge gas supply line 16, the purge gas can be accurately distributed without being affected by the secondary pressure because the pressure ratio P1/P2≧2 meeting a condition for sonic flow. Consequently, the dichlorosilane gas and the ammonia gas supplied into the processing vessel 1 are unable to flow through the outlets of the cleaning gas supply line 15 and the purge gas supply line 16 into the cleaning gas supply line 15 and the purge gas supply line 16, and hence the deposition of reaction products, such as silicon nitride and ammonium chloride, in the gas supply lines can be prevented. The pressure sensors PD1 and PD2 respectively placed in the main purge gas supply line 50 and the discharge line 34 measure pressures in the main purge gas supply line 50 and the discharge line 34, respectively. A controller, not shown, monitors the pressure ratio P1/P2, provides an alarm when the pressure ratio P1/P2 drops below two, and closes the valve V5 when P1 is less than P2.

After the film forming process has been completed, the shutoff valves V1 and V2 on the gas supply lines 13 and 14 are closed, the processing vessel 1 is evacuated, the purge gas is supplied through the purge gas supply line 16 into the processing vessel 1 to set the space in the processing vessel 1 at the atmospheric pressure, and then, the wafer boat 33 holding the wafers W is unloaded from the processing vessel 1. Since the purge gas flows continuously through the branch purge gas supply lines 51 into the processing vessel 1 before the wafer boat 33 holding the wafers W is unloaded from the processing vessel 1, the process gases, namely, the dichlorosilane gas and the ammonia gas, remaining in parts of the process gas supply lines 13 and 14 extending between the shutoff valves V1 and V2 and the processing vessel 1 can be quickly replaced with the purge gas.

A cleaning process is conducted after the wafer boat 33 holding the processed wafers W has been unloaded from the processing vessel. The wafers W are removed from the wafer boat 33, the empty wafer boat 33 is placed in the processing vessel 1, and then a cleaning gas is supplied from the cleaning gas source 12 through the cleaning gas supply line 15 into the processing vessel 1 to remove a film forming material and reaction products deposited on the inner surface of the processing vessel 1 and the wafer boat 33.

The valve V5 on the main purge gas supply line 50 is kept open during the cleaning process. The pressure in the processing vessel 1 corresponding to the secondary pressure P2 on the secondary side of the orifices 53 is, for example 5.3×104 Pa during the cleaning process. Therefore, the pressure ratio P1/P2 is two or above during the cleaning process, and the purge gas is supplied from the branch purge gas supply lines 51 to the gas supply lines 13 to 16 at equal low flow rates.

After the completion of the cleaning process, the next film forming process is started. In the piping system shown in FIG. 6, the purging gas is supplied at a low flow rate into parts of the gas supply lines 101 to 104 upstream of the shutoff valves V1 to V4 and hence the shutoff valves V3 and V4 on the gas supply lines 102 and 103 not participating in the film forming process are kept open during the film forming process. Therefore, the cleaning gas remaining in a long parts of the cleaning gas supply line 102 extending between a position above the first mass flow controller 105 in the gas box and the inlet port of the processing vessel 1 needs to be replaced with the purging gas before starting the film forming process. With the piping system in this embodiment according to the present invention, the purge gas is supplied at a low flow rate into the parts of the gas supply lines extending between the shutoff valves V1 to V4 and the processing vessel 1. Therefore, only the cleaning gas remaining in parts of the cleaning gas supply line 15 on the secondary side of the valve V3 needs to be replaced with the purging gas. An operation for replacing the cleaning gas remaining in the short part of the cleaning gas supply line 15 with the purging gas can be accomplished in a very short time.

Although the cleaning process and the film forming process are conducted continuously in the foregoing description, any different processes may be continuously conducted. For example, a first film forming process and a second film forming process different from the first film forming process may be continuously conducted or a monoatomic film forming process may be conducted by changing the process gases. For example, a continuous film forming process includes a first film forming process that forms a silicon nitride film in the manner mentioned above, and a second film forming process that forms a silicon oxide film on the silicon nitride film by supplying TEOS gas and oxygen gas as process gases through process gas supply lines for carrying those process gases into the processing vessel 1. In a monoatomic film forming process, dichlorosilane gas is supplied through the process gas supply line 13 into the processing vessel 1 to deposit a monoatomic silicon film on wafers W. Then, the valve V3 on the process gas supply line 13 is closed, the valve V on the process gas supply line 14 is opened and ammonia gas is supplied into the processing vessel 1 to deposit nitrogen on the monoatomic silicon film. Such steps are repeated several times to form a very thin silicon nitride film.

The above embodiment has the following advantages. Since the branch purge gas supply lines 51 are provided with the orifices 53 to supply the purge gas at a low rate for purging into the gas supply lines 13 to 16, the purge gas can be accurately equally distributed to the gas supply lines 13 to 16. Therefore, only the single mass flow controller 52 for controlling the total flow rate of the purge gas needs to be placed in the main purge gas supply line 50. Consequently, the equipment cost can be reduced, any error will not be produced in the total flow rate due to the accumulation of errors produced by a plurality of mass flow controllers and hence the processes are stable.

Since the purge gas is supplied at a lower flow rate into parts of the gas supply lines extending between the shutoff valves V1 to V4 and the processing vessel 1, the shutoff valves on the gas supply lines not participating in the process may be kept closed. Consequently, the process gases used by the preceding process and remaining in the gas supply lines can be replaced with the purging gas in a short time before starting the succeeding process, and hence the succeeding process can be started in a short time after the completion of the preceding process.

A piping system included in a semiconductor device fabricating system in a second embodiment according to the present invention will be described with reference to FIG. 4. The piping system shown in FIG. 4 is provided with a flow control unit including a mass flow meter 54 and an automatic pressure regulator 55 instead of a mass flow controller for controlling the total flow rate of a purge gas flowing through branch purge gas supply lines 51. A controller, not shown, controls the automatic pressure regulator 55 arranged downstream of the mass flow meter 54 on the basis of a measured flow rate measured by the mass flow meter 54 to control the total flow rate of the purge gas for pressure control. The primary pressure on the primary side of orifices 53 is controlled to control the flow rates of the purge gas flowing through the branch purge gas supply lines 51.

In a piping system shown in FIG. 5 included in a semiconductor device fabricating system in a third embodiment according to the present Invention, mass flow controllers 58 are placed in branch purge gas supply lines 51, respectively, instead of the orifices 53. Since the purge gas is supplied at a low flow rate through the mass flow controllers 58 to parts of gas supply lines extending between a processing vessel 1 and shutoff valves V1 to V4 placed in the gas supply lines, the shutoff valves V placed on the gas supply lines not participating in a process may be kept closed. Therefore, the process gases used for the process and remaining in the gas supply lines can be replaced with the purge gas in a very short time before starting the next process and hence the next process can be started in a short time after the completion of the preceding process.

If the purge gas heated at temperatures in the range of, for example 100 to 200° C. by a heating device, not shown, is supplied continuously Into the gas supply lines 12 to 16, the parts of the gas supply lines 13 to 16 extending between the processing vessel 1 and the shutoff valves V1 to V4 are heated, which prevents more effectively the deposition of reaction products in the shutoff valves V1 to V4 and in the gas supply lines.

In some cases, a cycle purging operation, which alternately repeats a step of supplying the purge gas through the purge gas supply line 16 into the processing vessel 1 and a step of evacuating the processing vessel 1, is executed to purge the process gases from the processing vessel 1 and to fill up the processing vessel 1 with the purging gas. When executing the cycle purging operation, the process gases remaining in parts of the process gas supply lines 13, 14 and 15 extending between the processing vessel 1 and the shutoff valves V1 to V3 must be completely replaced with the purge gas. According to the present invention, when executing the cycle purging operation, the purging gas can be supplied into the parts of the gas supply lines extending between the processing vessel 1 and the shutoff valves V1 to V3, and the process gases remaining in said parts of the process gas supply lines thus can be pushed out quickly into the processing vessel 1. Thus, the purging operation can be carried out effectively and quickly.

Although the invention has been described as applied to the batch type vertical semiconductor device fabricating systems, the present invention is applicable to other systems including single-wafer thermal processing systems and dry etching systems. 

1. A semiconductor device fabricating system comprising: a processing vessel; process gas supply lines each connected to the processing vessel to supply a process gas into the processing vessel; shutoff valves each placed in each of the process gas supply lines at a position adjacent to the processing vessel; a main purge gas supply line for carrying a purge gas; branch purge gas supply lines branched from the main purge gas supply line, each of the branch purge gas supply lines being connected to a part of each of the process gas supply lines extending between the shutoff valve and the processing vessel; a flow controller placed in the main purge gas supply line to control a sum of flow rates at which the purge gas flows through the branch purge gas supply lines; and orifices each placed in each of the branch purge gas supply lines, each of the orifices being configured so that a flow rate of the purge gas flowing through the orifice is determined according to a primary pressure on a primary side of the orifice when pressure ratio P1/P2, where P1 is a primary pressure on the primary side of the orifice, and P2 is a secondary pressure on a secondary side of the orifice, is not smaller than a predetermined value.
 2. The semiconductor device fabricating system according to claim 1, wherein the flow controller comprises a mass flow controller.
 3. The semiconductor device fabricating system according to claim 1, wherein the flow controller includes a flow measuring device, and a pressure regulating device for regulating the primary pressure P1 on the primary side of the orifices based on a measured flow rate measured by the flow measuring device.
 4. The semiconductor device fabricating system according to claim 1, wherein the predetermined value is not less than two.
 5. A semiconductor device fabricating system comprising: a processing vessel; process gas supply lines each connected to the processing vessel to supply a process gas into the processing vessel; shutoff valves each placed in each of the process gas supply lines at a position adjacent to the processing vessel; a main purge gas supply line for carrying a purge gas; branch purge gas supply lines branched from the main purge gas supply line, each of the branch purge gas supply lines being connected to a part of each of the process gas supply lines extending between the shutoff valve and the processing vessel; and flow controllers each placed in the each of the branch purge gas supply lines to control a flow rate at which the purge gas flows through each of the branch purge gas lines.
 6. A semiconductor device fabricating method of processing a substrate by a predetermined process in a processing vessel to fabricate semiconductor devices on the substrate by using process gases supplied through process gas supply lines connected to the processing vessel, said semiconductor device fabricating method comprising: supplying a purge gas through a main purge gas supply line and controlling the flow of the purge gas flowing through the main purge gas supply line; distributing the purge gas flowing through the main purge gas supply line to a plurality of branch purge gas supply lines; passing the purge gas distributed to the branch purge gas supply lines through orifices capable of determining, when pressure ratio P1/P2, where P1 is primary pressure on a primary side of the orifice and P2 is secondary pressure on a secondary side of the orifice, is not smaller than a predetermined value, a flow rate according to the primary pressure P1; supplying the purge gas passed through the orifices to parts of the process gas supply lines extending between the processing vessel and shutoff valves placed in the process gas supply lines at positions adjacent to the processing vessel; regulating pressure so that the pressure ratio P1/P2 is not smaller than a predetermined value; and closing at least one of the shutoff valves placed in the process gas supply lines to purge the process gas remaining in a part of the process gas supply line provided with the closed shutoff valve extending below the closed shutoff valve by the purge gas passed through the orifice.
 7. A semiconductor device fabricating method of processing a substrate by a predetermined process in a processing vessel to fabricate semiconductor devices on the substrate by using process gases supplied through process gas supply lines connected to the processing vessel, said semiconductor device fabricating method comprising: supplying a purge gas through a main purge gas supply line; distributing the purge gas flowing through the main purge gas supply line to a plurality of branch purge gas supply lines; controlling flow rates of the purge gas flowing through the branch purge gas supply lines by flow control means respectively placed in the branch purge gas supply lines; supplying the purge gas distributed to the branch purge gas supply lines to parts of the process gas supply lines extending between the processing vessel and shutoff valves placed in the process gas supply lines at positions adjacent to the processing vessel, respectively; and closing at least one of the shutoff valves placed in the process gas supply lines to purge the process gas remaining in a part of the process gas supply line provided with the closed shutoff valve extending below the closed shutoff valve by the purge gas passed through the branch purge gas supply line. 